Oxide superconductor

ABSTRACT

Provided is an oxide superconductor in which superconducting layer is sandwiched between two blocking layers having different compositions. Available superconducting layers include a one-layer system having one Cu-O 2  sheet, a two-layer system having a mediating layer sandwiched between two Cu-O 2  sheets, and a three-layer system having mediating layers sandwiched individually between three Cu-O 2  sheets. 
     Since the blocking layers are of different compositions, seventy-seven kinds of oxide superconductors can be obtained.

FIELD OF THE INVENTION

The present invention relates to oxide superconductors adapted for useas magnet coil materials in nuclear fusion furnaces, electromagneticfluid generators, accelerators, rotary electrical apparatuses (electricmotors, generators, etc.). magnetic separators, magnetic floatingtrains, magnetic floating automobiles, magnetic floating elevators,nuclear magnetic resonance computed tomographs, magnetically-propelledships, electron beam exposure devices, single crystal manufacturingapparatuses, various laboratory devices, etc., suited for applicationswhich involve the problem of power loss in transmission lines,electrical energy storing devices, transformers, rectifiers, etc.,further adapted for use in various elements, such as Josephson devices,SQUID, superconducting transistors, superconducting microwavetransmission circuits, and furthermore, adapted for use as variousfunction materials, such as infrared detection materials, magneticshielding materials, etc.

BACKGROUND OF THE INVENTION

Conventionally approximately twenty kinds copper compound oxidesuperconductors with different crystal structures are known. Any ofthese copper compound oxide superconductors commonly includes, in itscrystal structure, Cu-O₂ sheets through which superconducting currentflows, and a stratified structure composed of repeated units eachincluding the Cu-O₂ sheet and another layer situated at a predetermineddistance therefrom.

In the case of the crystal structure of La₂ CuO₄, for example, repeatedunits each including an La₂ O₂ layer and a Cu-O₂ sheet are arranged inlayers in the direction of a c-axis (direction perpendicular to theCu-O₂ sheet), as shown in FIG. 1. In other words, one Cu-O₂ sheet issandwiched between earth two La₂ O₂ layers. This structure having oneCu-O₂ sheet between the aforesaid layers, will be referred to as aone-layer system, hereinafter.

In the case of this crystal structure, there is a slip for a 1/2 unitcell in each La₂ O₂ layer with respect to the directions of a- andb-axes (directions within the plane of the Cu-O₂ sheet).Crystallographically, therefore, two La₂ O₂ layers and two Cu-O₂ sheetsconstitute a repeated unit.

One-layer system oxide superconductors of this type include, forexample, Bi₂ Sr₂ CuO₆, Tl₂ Ba₂ CuO₆, Nd₂ CuO₄, and Pb₂ SrLaCu₂ O₆₊ δ,which is described in "Physica C," vol. 166, 1990, pp. 502 to 512.

In the case of the crystal structure of Y₁ Ba₂ Cu₃ O₇, moreover,repeated units each including a BaO-CuO-BaO layer, a first Cu-O₂ sheet,a Y layer, and a second Cu-O₂ sheet are arranged in layers in thedirection of the c-axis, as shown in FIG. 2. Therefore, a unit composedof the first Cu-O₂ sheet, Y layer, and second Cu-O₂ sheet is sandwichedbetween each two BaO-CuO-BaO layers. This structure having two Cu-O₂sheets in the aforesaid unit will be referred to as a two-layer system,hereinafter.

In the case of this crystal structure, in contrast with the case of theaforementioned La₂ CuO₄, there is no slip with respect to the directionsof tile a- and b-axes, so that the aforesaid repeated units are notdifferent from crystallographic versions.

Two-layer system oxide superconductors of this type include, forexample, Bi₂ Sr₂ Ca₁ Cu₂ O₈, Tl₂ Ba₂ CaCu₂ O₈ described in "Nature",vol. 332, Mar. 31, 1988, pp. 420 to 422, YBa₂ Cu₄ O₈ described in"Nature", vol. 334, July 14, 1988, pp. 141 to 143, Ba₂ YCu₃ O_(7-x)described in "Japanese Journal of Applied Physics", vol. 26, No. 5, May,1987, pp. L649 to La_(2-x) Ca_(1+x) Cu₂ O_(6-x/2+) δ described in"Materials Chemistry", vol. 7, 1982, pp. 413 to 427, and Pb₂ Sr₂ (R,Ca)₁ Cu₃ O_(8+y) (R: rare earth element) described in "Physica C", vol.157, 1989, pp. 124 to 130.

In the case of the crystal structure of Bi₂ Sr₂ Ca₂ Cu₃ O₁₀, repeatedunits each including a SrO-Bi₂ O₂ -SrO layer, a first Cu-O₂ sheet, afirst Ca layer, a second Cu-O₂ sheet, a second Ca layer, and a thirdCu-O₂ sheet are arranged in layers in the direction of the c-axis, asshown in FIG. 3. Therefore, a unit composed of the first Cu-O₂ sheet,first Ca layer, second Cu-O₂ sheet, second Ca layer, and third Cu-O₂sheet is sandwiched between each two SrO-Bi₂ O₂ -SrO layers. Thisstructure having three Cu-O₂ sheets in the aforesaid unit will bereferred to as a three-layer system, hereinafter.

Also in the case of this crystal structure, as in the case of theaforementioned La₂ CuO₄, there is a slip for a 1/2 unit cell in eachSrO-Bi₂ O₂ -SrO layer with respect to the directions of the a- andb-axes. Crystallographically, therefore, the aforesaid two repeatedunits constitute a repeated unit.

Three-layer system oxide superconductors of this type include, forexample, a Pb-Bi-Sr-Ca-Cu-O-based superconductor described in "JapaneseJournal of Applied Physics", vol. 28, No. 5, May, 1989, pp. L787 toL790, a Tl-Pb-Sr-Ca-Cu-O-based superconductor described in "Science",vol. 242, October, 1988, pp. 249 to 252, and Tl₁ Ca_(n-1) Ba₂ Cu_(n)O_(2n+3) (n=1, 2, 3) described in "Physical Review Letters", vol. 61,No. 6, August, 1988, pp. 750 to 753.

It is known that the greater the number of Cu-O₂ sheets in each unit, inthe aforementioned one-, two-, and three-layer system superconductors,the higher the superconducting transition temperature (Tc) of thematerials.

The inventors hereof analyzed the correlations between the Tc of thecopper oxide superconductors described above and the interlayerdistances between the Cu-02 sheets in their crystal structures, andpresented the results of this analysis in "Physica C", vol. 167, 1990,pp. 515 to 519.

Thereupon, the inventors hereof discovered that the shorter theinterlayer distances between the Cu-O₂ sheets of the crystal structures,the higher the value of Tc. In order to assign reasons for thisphenomenon, the inventors hereof proposed that other layers interposedbetween the Cu-O₂ sheets through which superconducting current flowsshould be classified into blocking layers and mediating layers as theyare studied.

In this case, the blocking layer, in the crystal structure, may beregarded as a layer for cutting the interaction between the Cu-O₂sheets, through which the superconducting current flows, with thedistance between the Cu-O₂ sheets not shorter than 6 angstroms, andfurther supplying carriers to the Cu-O₂ sheets to give the Cu-O₂ sheetsa function for a superconducting current flow. The mediating layer,which is interposed between the Cu-O₂ sheets having -2-valent electriccharge as a whole, may be regarded as a layer for neutralizing theelectric charge, thereby enabling the whole crystal structure to beformed, and causing an interaction between the Cu-O₂ sheets with thedistance between them not longer than 4 angstroms.

From this point of view, the one-layer system oxide superconductor shownin FIG. 1 can be considered to be constructed so that one Cu-O₂ sheetserving as a superconducting layer is sandwiched between each twoidentical La₂ O₂ blocking layers.

In the case of the two-layer system oxide superconductor shown in FIG.2, on the other hand, two blocking layers are formed individually ofidentical BaO-CuO-BaO layers, and the unit composed of the first Cu-O₂sheet, Y layer as a mediating layer, and second Cu-O₂ sheet, sandwichedbetween the blocking layers, functions as a superconducting layer.

In the case of the three-layer system oxide superconductor shown in FIG.3, the unit composed of the first Cu-O₂ sheet, first Ca layer as a firstmediating layer, second Cu-O₂ sheet, second Ca layer as a secondmediating layer, and third Cu-O₂ sheet sandwiched between each twoidentical SrO-Bi₂ O₂ -SrO(blocking) layers, and this unit functions as asuperconducting layer.

Thus, according to the concept proposed by the inventors hereof, thecrystal structure of the conventionally proposed copper oxidesuperconductors can be considered to be designed so that asuperconducting layer is sandwiched between each two identical blockinglayers, and it can be concluded that this superconducting layer iscomposed of one Cu-O₂ sheet, or of two (for a two-layer system) or three(for a three-layer system) Cu-O₂ sheets with a mediating layer betweenthem.

If the conventionally known copper oxide superconductors are viewed atthis angle, the blocking layers may be classified into the following 8types:

La₂ O₂ -type,

BaO-CuO-BaO-type,

BaO-CuO-CuO-BaO-type,

SrO-Bi₂ O₂ -SrO-type,

BaO-Tl₂ O₂ -BaO-type or BaO-TlO-BaO-type,

SrO-PbO-Cu-PbO-SrO-type,

SrO-(Pb, Cu)O-SrO-type or SrO-(Pb, Sr)O-SrO-type,

and

Ln₂ O₂ -type (Ln is selected from Nd, Sm, Eu, and Gd).

Further, the mediating layer may be formed of Ca. Sr, Y, Nd, Sm, Eu, Gd,Dy, Ho, Er, Tm, Yb, or Lu.

The materials of the one-layer system shown in FIG. 1 have blockinglayers of only one kind except those ones which include Ln₂ O₂ -typeblocking layers. In either of the two- and three-layer systems shown inFIGS. 2 and 3, moreover, the blocking layers in the crystal structuresare of only one kind.

Accordingly, the conventional copper oxide superconductors are limitedto about 20 kinds, so that fields of their industrial application arerestricted.

SUMMARY OF THE INVENTION

An object of the present invention is to provide copper oxidesuperconductors, in which the approximately twenty kinds ofconventionally found copper oxide superconductors can be increased toabout seventy-seven kinds, so that the materials can be applied to awider variety of fields.

Another object of the present invention is to provide copper oxidesuperconductors having Tc higher than that of conventional copper oxidesuperconductors.

According to the present invention, there is first provided an oxidesuperconductor comprising repeated units each including a first blockinglayer having a composition selected from the following group, a firstCu-O₂ sheet, a second blocking layer having a composition selected fromthe following group and different from the composition of the firstblocking layer, and a second Cu-O₂ sheet, arranged in layers in theorder named,

the group including:

La₂ O₂,

BaO-CuO-BaO,

BaO-CuO-CuO-BaO,

SrO-Bi₂ O₂ -SrO,

BaO-Tl₂ O₂ -BaO,

BaO-TlO-BaO,

SrO-PbO-Cu-PbO-SrO,

SrO-(Pb, Cu)O-SrO, and

SrO-(Pb, Sr)O-SrO.

This superconductor will hereinafter be referred to as a one-layersystem oxide superconductor. According to the present invention,moreover, there is provided an oxide superconductor comprising repeatedunits each including a first blocking layer having a compositionselected from the following group a, a first Cu-O₂ sheet, a firstmediating layer composed of elements selected from the following groupb, a second Cu-O₂ sheet, a second blocking layer having a compositionselected from the following group a and different from the compositionof the first blocking layer, a third Cu-O₂ sheet, a second mediatinglayer composed of elements selected from the following group b, and afourth Cu-O₂ sheet, arranged in layers in the order named,

the group a including:

La₂ O₂,

BaO-CuO-BaO,

BaO-CuO-CuO-BaO,

SrO-Bi₂ O₂ -SrO,

BaO-Tl₂ O₂ -BaO,

BaO-TlO-BaO,

SrO-PbO-Cu-PbO-SrO,

SrO-(Pb, Cu)O-SrO,

SrO-(Pb, Sr)O-SrO, and

Ln₂ O₂

(where Ln is selected from Nd, Sm, Eu and Gd),

the group b including:

Ca, St, Y, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb and Lu. Thissuperconductor will hereinafter be referred to as a two-layer systemoxide superconductor.

According to the present invention, furthermore, there is provided anoxide superconductor comprising repeated units each including a firstblocking layer having a composition selected from the following group a,a first Cu-O₂ sheet, a first mediating layer composed of elementsselected from the following group b, a second Cu-O₂ sheet, a secondmediating layer composed of elements selected from the following groupb, a third Cu-O₂ sheet, a second blocking layer having a compositionselected from the following group a and different from the compositionof the first blocking layer, a fourth Cu-O₂ sheet, a third mediatinglayer composed of elements selected from the following group b, a fifthCu-O₂ sheet, a fourth mediating layer composed of elements selected fromthe following group b, and a sixth Cu-O₂ sheet, arranged in layers inthe order named,

the group a including:

La₂ O₂,

BaO-CuO-BaO,

BaO-CuO-CuO-BaO,

SrO-Bi₂ O₂ -SrO,

BaO-Tl₂ O₂ -BaO,

BaO-TlO-BaO,

SrO-PbO-Cu-PbO-SrO,

SrO-(Pb, Cu)O-SrO,

SrO-(Pb, Sr)O-SrO, and

Ln₂ O₂ (where Ln is selected from Nd, Sm, Eu and Gd),

the group b including:

Ca, St, Y, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb and Lu. Thissuperconductor will hereinafter be referred to as a three-layer systemoxide superconductor.

In the oxide superconductor according to the present invention, Tethereof can be increased if the interlayer distance between the Cu-O₂sheets in the crystal structure is made shorter. The present inventionis based on an inference that the interlayer distance between the Cu-O₂sheets may possibly be restricted by the state of the blocking layersadjacent to the sheets.

As mentioned before, the blocking layers serve to supply the eartiers tothe Cu-O₂ sheets, as well as to cut off the interaction between theCu-O₂ sheets.

Each known copper oxide superconductor has blocking layers of the samecomposition. It can be inferred, however, that even materials whichinclude different kinds of blocking layer compositions can becomesuperconductors as long as they can fulfill the aforementionedfunctions. But it can be guessed that the presence of the different kindof blocking layers causes some crystal strain in the crystal structureobtained.

First, diagrams of these three kinds of oxide superconductors are shownin FIGS. 4, 5 and 6.

In the one-layer system oxide superconductor of FIG. 4, a first blockinglayer B11 having a composition selected from the aforesaid group, afirst Cu-O₂ sheet C11, a second blocking layer B12 having a compositiondifferent from that of the first blocking layer, and a second Cu-O₂sheet C12 are arranged in layers in the c-axis direction, in the ordernamed, thus constituting a repeated unit U1, and a Cu-O₂ sheet C11 (C12)sandwiched between two blocking layers B11 and B12 forms asuperconducting layer. Further, the Cu-O₂ sheet situated between thesetwo blocking layers B11 and B12 is a single layer, and minimum units L11and L12, which are necessary for superconductivity, constitute baseunits.

In the two-layer system oxide superconducting material of FIG. 5, afirst blocking layer B21 having a composition selected from theaforesaid group a, a first Cu-O₂ sheet C21, a first mediating layer M21composed of elements selected from the aforesaid group b, a second Cu-O₂sheet C22, a second blocking layer B22 having a composition differentfrom that of the first blocking layer, a third Cu-O₂ sheet C23, a secondmediating layer M22 composed of elements selected from the aforesaidgroup b, and a fourth Cu-O₂ sheet C24 are arranged in layers in thec-axis direction, in the order named, thus constituting a repeated unitU2, and a unit S21, which includes the first Cu-O₂ sheet C21, mediatinglayer M21, and second Cu-O₂ sheet C22, and a unit S22, which includesthe third Cu-O₂ sheet C23, second mediating layer M22, and fourth Cu-O₂sheet C24, form superconducting layers. In this case, L21 and L22constitute base units.

In the three-layer system oxide superconductor of FIG. 6, a firstblocking layer B31 having a composition selected from the aforesaidgroup a, a first Cu-O₂ sheet C31, a first mediating layer M31 composedof elements selected from the aforesaid group b, a second Cu-O₂ sheetC32, a second mediating layer M32 composed of elements selected from theaforesaid group b, a third Cu-O₂ sheet C33, a second blocking layer B32having a composition different from that of the first blocking layer, afourth Cu-O₂ sheet C34, a third mediating layer M33 composed of elementsselected from the aforesaid group b, a fifth Cu-O₂ sheet C35, a fourthmediating layer M34 composed of elements selected from the aforesaidgroup b, and sixth Cu-O₂ sheet C36 are arranged in layers in the c-axisdirection, in the order named, thus constituting a repeated unit U3, anda unit S31, which includes the first Cu-O₂ sheet C31, first mediatinglayer M31. second Cu-O₂ sheet C32, second mediating layer M32, and thirdCu-O₂ sheet C33, and a unit S32, which includes the fourth Cu-O₂ sheetC34, third mediating layer M33, fifth Cu-O₂ sheet C35, fourth mediatinglayer M34, and sixth Cu-O₂ sheet C36, form superconducting layers. Inthis case, L31 and L32 constitute base units.

In any of the above-described cases of the one- , two-, and three-layersystems, one repeated unit directly constitutes a crystallographicrepeated unit if neither of the first and second blocking layers isslipped with respect to a direction or directions (a-axis directionand/or b-axis direction) perpendicular to the c-axis. If either of thefirst and second blocking layers is slipped in the a-axis directionand/or b-axis direction, however, two repeated units constitute onecrystallographic repeated unit. If both of the first and second blockinglayers are slipped, and if the first and second blocking layers areslipped in the same manner, one repeated unit directly constitutes acrystallographic repeated unit. If the first and second blocking layersare slipped in different ways, however, two repeated units constituteone crystallographic repeated unit.

In the case of the oxide superconductors found so far, each of whichincludes only one kind of blocking layers, that is, in the case wherethe first and second blocking layers are identical with each other, theaforementioned base unit and repeated unit are identical.

In each of these oxide superconductors, the composition whichconstitutes each blocking layer is not always a stoichiometriccomposition on account of excess or deficiency of oxygen.

In the case of SrO-Bi₂ O₂ -SrO, for example, excessive oxygen is oftencontained in practice, and the composition of this blocking layer is Bi₂Sr₂ O₄₊ δ.

The same may be said of BaO-Tl₂ O₂ -BaO or BaO-TlO-BaO, and therespective compositions of these blocking layers are Tl₂ Ba₂ O₄₊ δ andTlBa₂ O₃₊ δ.

Also in the case of SrO-PbO-Cu-PbO-SrO, oxygen is often excessivelyintroduced in practice, and the composition of this blocking layer isPb₂ Sr₂ CuO₄₊ δ.

In the cases of other compositions, that is. BaO-CuO-BaO orBaO-CuO-CuO-BaO, La₂ O₂, SrO-(Pb, Cu)O-SrO, SrO-(Pb, Sr)O-SrO, and Ln₂O₂, on the other hand, oxygen is often deficient, and the respectivecompositions of these blocking layers are Ba₂ CuO₃₋ δ, Ba₂ Cu₂ O₄₋ δ,La₂ O₂₋ δ, (Pb, Cu)Sr₂ O₃₋ δ, (Pb, Sr)Sr₂ O₃₋ δ, and Ln₂ O₂₋ δ.

In any of the aforesaid compositions, the length of its crystal cell isequal or approximately equal to the Cu-O bond length of the Cu-O₂sheets. In forming the whole crystal structure by the method mentionedbelow, therefore, the blocking layers of these compositions fit theCu-O₂ sheets, thus stabilizing the crystal structure.

In forming each superconductor with the blocking layers of thesecompositions, different compositions are selected for the first andsecond blocking layers mentioned above. This is because it is estimated,although without any obvious reasons, that if the superconducting layeris sandwiched between the different kinds of blocking layers, a strainis caused in the superconducting layer, so that the Tc is higher than inthe case where the superconductor is sandwiched between blocking layersof the same kind.

If the composition used for each blocking layer of the two- andthree-layer systems is Ln₂ O₂, moreover, only one of the aforesaidelements may be used as Ln, or two or more may be suitably selected foruse.

Likewise, one or two or more elements may be selected from the group b.

In the oxide superconductors of the present invention, whether the one-,two-, or three-layer type, superconducting charge carriers are holes. Asin the case of the known copper oxide superconductors, therefore,superconductors are obtained when the hole density of the Cu-O₂ sheet isnot lower than 0.01 or not higher than 0.5 per Cu atom.

In order to adjust the carrier concentration to the aforesaid ranges,the oxygen content in the composition used may deviate somewhat from itsstoichiometric value, or some of the cations which constitute thecomposition may be substituted by other cations in forming the blockinglayers by the method mentioned below.

In oxide superconductors one of whose blocking layers consist ofSrO-PbO-Cu-PbO-SrO, the valency of Cu in the blocking layer, which makesno change, is +1, so that the hole density per Cu atom is calculatedtaking valency of Cu as +1.

In this calculation, moreover, all the respective valency of La, Bi, Tl,Ln (Nd, Sm, Eu, Gd, Dy, Ho, Tm, Yb and Lu) are all regarded as +3, allthe respective valency of Ba, Sr and Ca as +2, and the valency of 0 as-2. Pb can take valency of +2 and +4. In this case, therefore, thevalency of Pb is regarded as +3, the average of +2 and +4. In formingblocking layers of SrO-PbO-Cu-PbO-SrO, however, the valency of Pb isregarded as +2.

The holes are supplied mainly by changing the heat treatment conditionsunder various oxygen partial pressures to control the oxygen content inthe crystal structure, during the manufacture of an oxidesuperconductor, or by substitution of some of the elements in theblocking layers.

In the case of heat treatment under the various oxygen partialpressures, for example, the oxygen partial pressure is varied within therange 0.001 to 1,000 arm. When the oxygen partial pressure is lower than1 arm., the superconductor is annealed for from 1 to 100 hours at atemperature ranging from about 300° C. to less than the melting point ofthe material, and is then rapidly cooled to the temperature of liquidnitrogen. By doing this, an oxygen deficiency is caused to reduce theoxygen content, whereby the hole concentration is lowered.

When the oxygen partial pressure is higher than 1 atm., on the otherhand, the superconductor is annealed for from i to 100 hours at atemperature ranging from about 300° C. to less than the melting point ofthe material. Then, the oxygen deficiency is eliminated by slowlycooling the superconductor in a furnace, or excessive oxygen isintroduced into the furnace to increase the oxygen content, whereby thehole concentration is increased. Moreover, the hole concentration can beincreased by increase of oxygen content by mixing ozone with oxygen inan oxygen atmosphere during the heat treatment.

Since this hole concentration control method can be carried out as aseparate process even after the intended crystal structure ismanufactured, it is particularly suited for the case where the holes arejust enough in number so that no crystal can be obtained unless theelectric charge on the whole crystal is balanced, or the case where therange of the partial pressure of oxygen in the atmosphere must belimited in order to grow the crystal.

The following is a description of a method for controlling the holeconcentration by the substitution of some of the elements in theblocking layers.

In the case of La₂ O₂, for example, holes can be supplied bysubstituting +2-valent Ba, Sr or Ca or +1-valent Na for some of+3-valent La.

In the case of BaO-CuO-BaO or BaO-CuO-CuO-BaO, the hole concentrationcan be controlled by substituting a +1-valent alkaline metal, such asNa, for Ba to supply holes, or by substituting Sr or Pb for some of Bato change the atom packing state of the crystal structure, therebychanging the facility of oxygen introduction. Also, the holeconcentration can be controlled by substituting Al or Ga for Cu.

In the case of SrO-Bi₂ O₂ -SrO, the hole concentration can be controlledby substituting +2-valent Pb for some of +3-valent Bi to supply holes,or by substituting +3-valent La for some of +2-valent Sr to reduceholes.

In the case of BaO-Tl₂ O₂ -BaO or BaO-TlO-BaO, the hole concentrationcan be controlled by substituting +2-valent Pb for some of +3-valent T1to supply holes, or by substituting +3-valent La for some of +2-valentBa to change the atom packing state of the crystal structure, therebychanging the facility of oxygen introduction.

In the case of SrO-PbO-Cu-PbO-SrO, SrO-(Pb, Cu)O-SrO, or SrO-(Pb,Sr)O-SrO, the hole concentration can be controlled by substituting+3-valent La for some of +2-valent Sr to reduce holes, or bysubstituting Ba or Ca for some of Sr to change the atom packing state ofthe crystal structure, thereby changing the facility of oxygenintroduction.

In the case of Ln₂ O₂, the carrier concentration can be controlled bysubstituting a +2-valent alkaline earth metal, such as Ca or Mg, forsome of +3-valent Ln to supply holes, or by substituting +4-valent Ce orTh for some of +3-valent Ln to reduce holes.

In the cases of two- and three-layer system oxide superconductors,moreover, the hole concentration can be controlled by changing thecombination ratios between +2-valent Ca or Sr and +3-valent Y, Nd, Sm,Eu, Gd, Dy, Ho, Er, Tm, Yb and Lu in selecting the elements for themediating layers from the aforesaid group b.

The oxide superconductors of the present invention will now beenumerated with reference to models of the repeating units (U1, U2 andU3) shown in FIGS. 4 to 6.

These models are combinations of the blocking layers, Cu-O₂ sheets, andmediating layers. The compositions of the blocking layers are expressedin the same manner as the composition group for the one-layer system andthe group a for the two- and three-layer systems. Actually, however, theoxygen content may be somewhat deviated from its stoichiometric value,or some cations may be replaced, in order to adjust the carrierconcentration, as mentioned before. For the two- and three-layer systemoxide superconductors, moreover, the mediating layers composed of theelements selected from the group b are designated by M's. Further, theone-, two-, and three-layer system oxide superconductors are designatedindividually by serial numbers, e.g., "1-16," "2-10," and "3-5."

There are 21 kinds of one-layer system oxide superconductors as follows:

1--1: BaO-CuO-BaO/Cu-O₂ /La₂ O₂ /Cu-O₂,

1-2: BaO-CuO-CuO-BaO/Cu-O₂ /La₂ O₂ /Cu-O₂,

1-3: BaO-CuO-CuO-BaO/Cu-O₂ /BaO-CuO-BaO/Cu-O₂,

1-4: SrO-Bi₂ O₂ -SrO/Cu-O₂ /La₂ O₂ /Cu-O₂,

1-5: SrO-Bi₂ O₂ -SrO/Cu-O₂ /BaO-CuO-BaO/Cu-O₂,

1-6: SrO-Bi₂ O₂ -SrO/Cu-O₂ /BaO-CuO-CuO-BaO/Cu-O₂,

1-7: (BaO-Tl₂ O₂ -BaO) or (BaO-TlO-BaO)/Cu-O₂ /La₂ O₂ /Cu-O₂,

1-8: (BaO-Tl₂ O₂ -BaO) or (BaO-TlO-BaO)/Cu-O₂ /BaO-CuO-BaO/Cu-O₂,

1-9: (BaO-Tl₂ O₂ -BaO) or (BaO-TlO-BaO)/Cu-O₂ /BaO-CuO-CuO-BaO/Cu-O₂,,

1-10: (BaO-Tl₂ O₂ -BaO) or (BaO-TlO-BaO)/Cu-O₂ /SrO-Bi₂ O₂ -SrO/Cu-O₂,

1-11: SrO-PbO-Cu-PbO-SrO/Cu-O₂ /La₂ O₂ /Cu-O₂,

1-12: SrO-PbO-Cu-PbO-SrO/Cu-O₂ /BaO-CuO-BaO/Cu-O₂,

1-13: SrO-PbO-Cu-PbO-SrO/Cu-O₂ /BaO-CuO-CuO-BaO/Cu-O₂,

1-14: SrO-PbO-Cu-PbO-SrO/Cu-O₂ /SrO-Bi₂ O₂ -SrO/Cu-O₂,

1-15: SrO-PbO-Cu-PbO-SrO/Cu-O₂ /(BaO-Tl₂ O₂ -BaO) or(BaO-TlO-BaO)/Cu-O₂,

1-16: (SrO-(Pb, Cu)O-SrO) or SrO-(Pb, Sr)O-SrO/Cu-O₂ /La₂ O₂ /Cu-O₂,

1-17: (SrO-(Pb, Cu)O-SrO) or SrO-(Pb, Sr)O-SrO/Cu-O₂ /BaO-CuO-BaO/Cu-O₂,

1-18: (SrO-(Pb, Cu)O-SrO) or SrO-(Pb, Sr)O-SrO/Cu-O₂/BaO-CuO-CuO-BaO/Cu-O₂,

1-19: (SrO-(Pb, Cu)O-SrO) or SrO-(Pb, Sr)O-SrO/Cu-O₂ /SrO-Bi₂ O₂-SrO/Cu-O₂,

1-20: (SrO-(Pb, Cu)O-SrO) or SrO-(Pb, Sr)O-SrO/Cu-O₂ /(BaO-Tl₂ O₂ -BaO)or (BaO-TlO-BaO)/Cu-O₂,

1-21: ( SrO-(Pb, Cu)O-SrO) or SrO-(Pb, Sr)O-SrO/Cu-O₂/SrO-PbO-Cu-PbO-SrO/Cu-O₂.

There are 28 kinds of two-layer system oxide superconductors as follows:

2-1: BaO-CuO-BaO/Cu-O₂ /M/Cu-O₂ /La₂ O₂ /M/Cu-O₂,

2--2: BaO-CuO-CuO-BaO/Cu-O₂ /M/Cu-O₂ /La₂ O₂ /Cu-O₂ /M/Cu-O₂,

2-3: BaO-CuO-CuO-BaO/Cu-O₂ /M/Cu-O₂ /BaO-CuO-BaO/Cu-O₂ /M/Cu-O₂,

2-4: SrO-Bi₂ O₂ -SrO/Cu-O₂ /M/Cu-O₂ /La₂ O₂ /Cu-O₂ /M/Cu-O₂,

2-5: SrO-Bi₂ O₂ -SrO/Cu-O₂ /M/Cu-O₂ /BaO-CuO-BaO/Cu-O_(O) ₂ /M/Cu-O₂,

2-6: SrO-Bi₂ O₂ -SrO/Cu-O₂ /M/Cu-O₂ /BaO-CuO-CuO-BaO/Cu-O₂ /M/Cu-O₂,

2-7: (BaO-Tl₂ O₂ -BaO) or (BaO-TlO-BaO)/Cu-O₂ /M/Cu-O₂ /La₂ O₂ /Cu-O₂/M/Cu-O₂,

2-8: (BaO-Tl₂ O₂ -BaO) or (BaO-TlO-BaO)/Cu-O₂ /M/Cu-O₂/BaO-CuO-BaO/Cu-O₂ /M/Cu-O₂,

2-9: (BaO-Tl₂ O₂ -BaO) or (BaO-TlO-BaO)/Cu-O₂ /M/Cu-O₂/BaO-CuO-CuO-BaO/Cu-O₂ /M/Cu-O₂,

2-10: (BaO-Tl₂ O₂ -BaO) or (BaO-TlO-BaO)/Cu-O₂ /M/Cu-O₂ /SrO-Bi₂ O₂-SrO/Cu-O₂ /M/Cu-O ₂,

2-11: SrO-PbO-Cu-PbO-SrO/Cu-O₂ /M/Cu-O₂ /La₂ O₂ /Cu-O₂ /M/Cu-O₂,

2-12: SrO-PbO-Cu-PbO-SrO/Cu-O₂ /M/Cu-O₂ /BaO-CuO-BaO/Cu-O₂ /M/Cu-O₂,

2-13: SrO-PbO-Cu-PbO-SrO/Cu-O₂ /M/Cu-O₂ /M/Cu-O₂ /BaO-CuO-CuO-BaO/Cu-O₂/M/Cu-O₂,

2-14: SrO-PbO-Cu-PbO-SrO/Cu-O₂ /M/Cu-O₂ /SrO-Bi₂ O₂ -SrO/Cu-O₂ /M/Cu-O₂,

2-15: SrO-PbO-Cu-PbO-SrO/Cu-O₂ /M/Cu-O₂ /BaO-Tl₂ O₂ -BaO) or(BaO-TlO-BaO)/Cu-O₂ /M/Cu-O₂,

2-16: (SrO-(Pb, Cu)O-SrO) or SrO-(Pb, Sr)O-SrO/Cu-O₂ /M/Cu-O₂ /La₂ O₂/Cu-O₂ /M/Cu-O₂,

2-17: (SrO-(Pb, Cu)O-SrO) or SrO-(Pb, Sr)O-SrO/Cu-O₂ /M/Cu-O₂/BaO-CuO-BaO/Cu-O₂ /M/Cu-O₂,

2-18: (SrO-(Pb, Cu)O-SrO) or SrO-(Pb, Sr)O-SrO/Cu-O₂ /M/Cu-O₂/BaO-CuO-CuO-BaO/Cu-O₂ /M/Cu-O₂,

2-19: (SrO-(Pb, Cu)O-SrO) or SrO-(Pb, Sr)O-SrO/Cu-O₂ /M/Cu-O₂ /SrO-Bi₂O₂ -SrO/Cu-O₂ /M/Cu-O₂,

2-20: (SrO-(Pb, Cu)O-SrO) or SrO-(Pb, Sr)O-SrO/Cu-O₂ /M/Cu-O₂ /(BaO-Tl₂O₂ -BaO) or (BaO-TlO-BaO)/Cu-O ₂ /M/Cu-O₂,

2-21: (SrO-(Pb, Cu)O-SrO) or SrO-(Pb, Sr)O-SrO/Cu-O₂ /M/Cu-O₂/SrO-PbO-Cu-PbO-SrO/Cu-O₂ /M/Cu-O₂,

2-22: Ln₂ O₂ /Cu-O₂ /M/Cu-O₂ /La₂ O₂ /Cu-O₂ //M/Cu-O₂,

2-23: Ln₂ O₂ /Cu-O₂ /M/Cu-O₂ /BaO-CuO-BaO/Cu-O₂ /M/Cu-O₂,

2-24: Ln₂ O₂ /Cu-O₂ /M/Cu-O₂ /BaO-CuO-CuO-BaO/Cu-O₂ /M/Cu-O₂,

2-25: Ln₂ O₂ /Cu-O₂ /M/Cu-O₂ /SrO-Bi₂ O₂ -SrO/Cu-O₂ /M/Cu-O₂,

2-26: Ln₂ O₂ /Cu-O₂ /M/Cu-O₂ /(BaO-Tl₂ O₂ -BaO) or (BaO-TlO-BaO)/Cu-O₂/M/Cu-O₂,

2-27: Ln₂ O₂ /Cu-O₂ /M/Cu-O₂ /SrO-PbO-Cu-PbO-SrO/Cu-O₂ /M/Cu-O₂,

2-28: Ln₂ O₂ /Cu-O₂ /M/Cu-O₂ /(SrO-(Pb, Cu)O-SrO) or SrO-(Pb,Sr)O-SrO/Cu-O₂ /M/Cu-O₂.

There are 28 kinds of three-layer system oxide superconductors asfollows:

3-1: BaO-CuO-BaO/Cu-O₂ /M/Cu-O₂ /M/Cu-O₂ /La₂ O₂ /Cu-O₂ /M/Cu-O₂/M/Cu-O₂,

3-2: BaO-CuO-CuO-BaO/Cu-O₂ /M/Cu-O₂ /M/Cu-O₂ /La₂ O₂ /Cu-O₂ /M/Cu-O₂/M/Cu-O₂,

3--3: BaO-CuO-CuO-BaO/Cu-O₂ /M/Cu-O₂ /M/Cu-O₂ /BaO-CuO-BaO/Cu-O₂/M/Cu-O₂ /M/Cu-O₂,

3-4: SrO-Bi₂ O₂ -SrO/Cu-O₂ /M/Cu-O₂ /M/Cu-O₂ /La₂ O₂ /Cu-O₂ /M/Cu-O₂/M/Cu-O ₂,

3-5: SrO-Bi₂ O₂ -SrO/Cu-O₂ /M/Cu-O₂ /M/Cu-O₂ /BaO-CuO-BaO/Cu-O₂ /M/Cu-O₂/M/Cu-O₂,

3-6: SrO-Bi₂ O₂ -SrO/Cu-O₂ /M/Cu-O₂ /M/Cu-O₂ /BaO-CuO-CuO-BaO/Cu-O₂/M/Cu-O=/M/Cu-O₂,

3-7: (BaO-Tl₂ O₂ -BaO) or (BaO-TlO-BaO)/Cu-O₂ /M/Cu-O₂ /M/Cu-O₂ /La₂ O₂/Cu-O₂ /M/ Cu-O₂ /M/Cu-O₂ /M/Cu-O₂,

3-8: (BaO-Tl₂ O₂ -BaO) or (BaO-TlO-BaO)/Cu-O₂ /M/Cu-O₂ /M/Cu-O₂/BaO-CuO-BaO/Cu-O₂ /M/Cu-O₂ /M/Cu-O₂,

3-9: (BaO-Tl₂ O₂ -BaO) or (BaO-TlO-BaO)/Cu-O₂ //M/Cu-O₂ /M/Cu-O₂/BaO-CuO-CuO-BaO/Cu-O₂ /M/Cu -O₂ /M/Cu-O₂,

3-10: (BaO-Tl₂ O₂ -BaO) or (BaO-TlO-BaO )/Cu-O₂ /M/Cu-O₂ /M/Cu-O₂/SrO-Bi₂ O₂ -SrO/Cu-O ₂ /M/Cu-O₂ /M/Cu-O₂,

3-11: SrO-PbO-Cu-PbO-Sr/Cu-O₂ /M/Cu-O₂ /M/Cu-O₂ /La₂ O₂ /Cu-O₂ /M/Cu-O₂/M/Cu-O₂,

3-12: SrO-PbO-Cu-PbO-SrO/Cu-O₂ /M/Cu-O₂ /M/Cu-O₂ /BaO-CuO-BaO/Cu-O₂/M/Cu-O₂ /M/Cu-O₂,

3-13: SrO-PbO-Cu-PbO-SrO/Cu-O₂ /M/Cu-O₂ /M/Cu-O₂ /BaO-CuO-CuO-BaO/Cu-O₂/M/Cu-O₂ /M/Cu-O₂,

3-14: SrO-PbO-Cu-PbO-SrO/Cu-O₂ /M/Cu-O₂ /M/Cu-O₂ /SrO-Bi₂ O₂ -SrO/Cu-O₂/M/Cu-O₂ /M/Cu-O ₂,

3-15: SrO-PbO-Cu-PbO-SrO/Cu-O₂ /M/Cu-O₂ /M/Cu-O₂ /(BaO-Tl₂ O₂ -BaO) or(BaO-TlO-BaO)/Cu-O₂ /M/Cu-O₂ /M/Cu-O₂,

3-16: (SrO-(Pb, Cu)O-SrO) or SrO-(Pb, Sr)O-SrO/Cu-O₂ /M/Cu-O₂ /M/Cu-O₂/La₂ O₂ /Cu-O₂ /M/Cu-O ₂ /M/Cu-O₂,

3-17: (SrO-Pb, Cu)O-SrO) or SrO-(Pb, Sr)O-SrO/Cu-O₂ /M/Cu-O₂ /M/Cu-O₂/BaO-CuO-BaO/Cu-O₂ /M/Cu-O₂ / M/Cu-O₂,

3-18: (SrO-(Pb, Cu)O-SrO) or SrO-(Pb, Sr)O-SrO/Cu-O₂ /M/Cu-O₂ /M/Cu-O₂/BaO-CuO-CuO-BaO/Cu-O₂ /M/Cu-O₂ /M/Cu-O₂,

3-19: (SrO-(Pb, Cu)O-SrO) or SrO-(Pb, Sr)O-SrO/Cu-O₂ /M/Cu-O₂ /M/Cu-O₂/SrO-Bi₂ O₂ -SrO/Cu-O₂ /M/Cu-O₂ /M/Cu-O₂,

3-20: (SrO-(Pb, Cu)O-SrO) or SrO-(Pb, Sr)O-SrO/Cu-O₂ /M/Cu-O₂ /M/Cu-O₂/(BaO-Tl₂ O₂ -BaO) or (BaO-TlO-BaO)/Cu-O₂ /M/Cu-O₂ /M/Cu-O₂,

3-21: (SrO-(Pb, Cu)O-SrO) or SrO-(Pb, Sr)O-SrO/Cu-O₂ /M/Cu-O₂ /M/Cu-O₂/SrO-PbO-Cu-PbO-SrO/Cu-O₂ /M/Cu-O ₂ /M/Cu-O₂,

3-22: Ln₂ O₂ /Cu-O₂ /M/Cu-O₂ /M/Cu-O₂ /La₂ O₂ /Cu-O₂ /M/Cu-O₂ /M/Cu-O₂ ,

3-23: Ln₂ O₂ /Cu-O₂ /M/Cu-O₂ /M/Cu-O₂ /BaO-CuO-BaO/Cu-O₂ /M/Cu-O₂/M/Cu-O₂,

3-24: Ln₂ O₂ /Cu-O₂ /M/Cu-O₂ /M/Cu-O₂ /BaO-CuO-CnO-BaO/Cu-O₂ /M/Cu-O₂/M/Cu-O₂,

3-25: Ln₂ O₂ /Cu-O₂ /M/Cu-O₂ /M/Cu-O₂ /SrO-Bi₂ O₂ -SrO/Cu-O₂ /M/Cu-O₂/M/Cu -O₂,

3-26: Ln₂ O₂ /Cu-O₂ /M/Cu-O₂ /M/Cu-O₂ /(BaO-Tl₂ O₂ -BaO) or(BaO-TlO-BaO)/Cu-O₂ /M/Cu-O₂ /M/Cu-O₂,

3-27: Ln₂ O₂ /Cu-O₂ /M/Cu-O₂ /M/Cu-O₂ /SrO-PbO-Cu-PbO-SrO/Cu-O₂ /M/Cu-O₂/M/Cu-O₂,

3-28: Ln₂ O₂ /Cu-O₂ /M/Cu-O₂ /M/Cu-O₂ /(SrO-(Pb, Cu)O-SrO) or SrO-(Pb,Sr)O-SrO/Cu-O₂ /M/Cu-O₂ /M/Cu-O₂.

The oxide superconductor of the present invention can be prepared byvarious methods.

For example, the superconductor can be prepared by the well-known powdermixing method. Preferably, it may be prepared by various depositionmethods capable of deposition control of elements on atomic order, suchas the electron beam deposition method, laser deposition method, etc.,or various sputtering methods, such as the magnetron sputtering method.Also, it may be prepared by the chemical vapor deposition method usinghalides, organic metals, etc., atomization method using nitrates,organic acids, or application method using alcoxides and the like.

If the total pressure of the atmosphere during the manufacture is 1 atm.or less, as in the cases of the electron beam deposition, laserdeposition, magnetron sputtering, chemical vapor deposition method,etc., the oxygen deficiency in the superconductor can be covered asaforesaid by mixing ozone with the atmosphere.

Among these manufacturing methods, the laser deposition method in theoxygen atmosphere is particularly preferable, since layers of intendedcompositions can be formed by deposition under fine control according tothis method.

This laser deposition method is described in, for example, "JapaneseJournal of Applied Physics", vol. 27, No. 7, July, 1988, pp. L1293 toL1296, or "Appl. Phys. Lett.", vol. 54, No. 18, May, 1989, pp. 1802 to1804, and "Appl. Phys. Lett.", vol. 57, No. 2, July 9, 1990, pp. 198 to200.

In general, the oxide superconductors of the present invention areprepared by the laser deposition method as follows.

First, an intended crystal structure is designed, and the respectivecompositions of the first and second blocking layers are selected. Then,sintered bodies having the respective compositions of the individualblocking layers are prepared. Also, a sintered body of Cu or Cu₂ (sic)and the elements for the mediating layers are prepared for thesuperconducting layers.

In the case of the one-layer system oxide superconductor, it isnecessary only that sintered bodies for the individual blocking layersand a sintered body of Cu or CuO₂ (sic) are prepared. In the cases ofthe two- and three-layer system oxide superconductors, moreover,sintered bodies containing CuO₂ (sic) and the elements for the mediatinglayers in a desired ratio may be prepared for the superconductingmaterials.

These individual sintered bodies are separately located in a chamber tobe used as targets, and a single crystal substrate of, e.g., MgO (100),heated up to a desired temperature, are opposed to the targets. In thisstate, the chamber is loaded with an oxygen atmosphere having a desiredoxygen partial pressure, and a pulsed excimer laser with a desiredintensity is applied to the targets.

At this time, the laser is applied in the order of the target for thefirst blocking layer, target for a superconducting layer, target for thesecond blocking layer, target for another superconducting layer, . . . .

As a result, a film including repeated units each composed of the firstblocking layer, superconducting layer, second blocking layer, andsuperconducting layer is formed on the surface of the single crystalsubstrate. Thereafter, the obtained film is subjected to heat treatmentunder the desired oxygen partial pressure, as mentioned before, so thatcarrier concentration is adjusted, whereby the superconductor isobtained.

In order to form this crystal structure, the repeated units should beelectrically neutral. This is because if the electric charge of thewhole repeated units is not neutral, the bulk body having crystalstructure cannot grow.

If each layer is formed on the basis of a designed crystal structure,the repeated units obtained are not always electrically neutral, andhave a positive or negative electric charge as a whole. This can beestimated beforehand from the electric charges of the aforesaidconstituent elements.

Table 1 shows the results of calculation of the respective electriccharges of repeated units (Case 1) of a one-layer system oxidesuperconductor and a two- or three-layer system oxide superconductorwhose mediating layers are formed of Ca, repeated units (Case 2) of atwo-layer system oxide superconductor whose mediating layers are formedof Y, and repeated units (Case 3) of a three-layer system oxidesuperconductor whose mediating layers are formed of Y.

                  TABLE 1                                                         ______________________________________                                        No.    Case 1        Case 2    Case 3                                         ______________________________________                                         1     -1            +1        +3                                              2     -2             0        +2                                              3     -3            -1        +1                                              4      0            +2        +4                                              5     -1            +1        +3                                              6     -2             0        +2                                              7      0 or -1      +2 or -1  +4 or +3                                        8     -1 or -2      +1 or  0  +3 or +2                                        9     -2 or -3       0 or -1  +2 or +1                                       10      0 or -1      +2 or +1  +4 or +3                                       11     -1            +1        +3                                             12     -2             0        +2                                             13     -3            -1        +1                                             14     -1            +1        +3                                             15     -1 or -2      +1 or  0  +3 or +2                                       16     -2             0        +2                                             17     -3            -1        +1                                             18     -4            -2        0                                              19     - 2            0        +2                                             20     -2 or -3       0 or -1  +2 or +1                                       21     -3            -1        +1                                             ______________________________________                                    

Based on this table, therefore, partial substitution of the constituentelements of the mediating layers or other elements in the compositionconstituting each blocking layer can be adopted, and the targetcomposition can be selected so that the electric charge of the wholerepeated units is 0.

In preparing a repeated unit No. 7 of Case 3, for example, the electriccharge of the whole repeated unit can be decreased to 0 by substitution+3-valent Y for +2-valent Ca which form meditating layer.

Whether or not the material thus obtained is superconductive can bedetermined by cooling this material to a very low temperature andmeasuring its electrical resistance or magnetic susceptibility.

Even at room temperature, however, it can be analyzed by the methodmentioned below. The following is a description of this method.

The optical properties of obtained samples are measured underpredetermined conditions by means of a spectroellipsometry, whereupon areal part ε₁ and an imaginary part ε₂ of a complex dielectric functiongiven by ε*=ε₁ +ε₂ i (i: imaginary unit) are simultaneously obtained.

The respective values of the real and imaginary parts ε₁ and ε₂ areplotted with respect to the measurement wave-number, and whether or notthe value of the real part ε₁ passes zero on the resulting curve isread. If the value of the real part ε₁ for material passes zero, thenthe material is superconducting.

Then, a reciprocal function a* (=1/ε*) of the aforesaid complexdielectric function ε* is calculated. In this case, this reciprocalfunction is also a complex function, which is given by a*=a₁ +a₂ i (i:imaginary).

The respective values of real and imaginary pares a₁ and a₂ of thereciprocal function a* are plotted with respect to the aforesaidmeasurement wave-number. A curve representing the imaginary part a₂ fora superconductive material has a clear peak at almost; the samewave-number which gives ε₁ =o in the aforesaid complex dielectricfunction. For a material which is not superconducting, no such peakappears, or if any, the peak is shifted to the low-wave-number side, andis broad.

Thus, if the curve representing the real part ε₁ of the aforesaidcomplex dielectric function passes the zero value, and if the curverepresenting the imaginary part a₂ of the reciprocal function of thecomplex dielectric function has its peak value at almost the samewave-number for ε₁ =0, then the material is judged to besuperconducting.

For example, an oxide superconductor A, which has a compositionexpressed as Bi₂ Sr₂ CaCu₂ O_(y) and Tc=85 K, and a non-superconductingmaterial B, which has a composition expressed as Bi₂ Sr₂ CuO₂ and is notsuperconducting unless Tc=0 K is obtained, were prepared, and therespective complex dielectric functions of these materials were measuredunder the following conditions by using a phase difference measuringapparatus (NPDM-1000 from Nippon Kogaku K.K.).

Spectroscope: M-70,

Light source: Halogen lamp,

Sensor: Si and Ge,

Polarizer and analyzer: Gran-Thomson

Number of revolutions of analyzer: 2,

Angie of incidence: 80°,

Measurement wave-number: 7,000 to 25,000 cm⁻¹,

FIG. 7 shows the relationships between the real and imaginary parts ε₁and ε₂ of the complex dielectric function ε* of the material A and themeasurement wave-number, and FIG. 8 shows the relationships between thereal and imaginary parts a₁ and a₂ of the reciprocal function a* of thecomplex dielectric function ε* of the material A and the measurementwave-number. In this drawing, open circles and closed circles representthe real and imaginary parts, respectively.

As seen from FIG. 7, the curve representing the real part ε₁ passes thezero value when the wave-number is nearly 8,100 cm⁻¹. As seen from FIG.8, moreover, the curve representing the imaginary part a₂ has its peakvalue when the wave-number is nearly 8,100 cm⁻¹.

On the other hand, FIG. 9 shows the relationships between-the real andimaginary parts ε₁ and ε₂ of the complex dielectric function ε* of thematerial B and the measurement wave-number, and FIG. 10 shows therelationships between the real and imaginary parts a₁ and a₂ of thereciprocal function a* of the complex dielectric function ε* of thematerial B and the measurement wave-number. In this drawing, opencircles and closed circles represent the real and imaginary parts,respectively.

In the case of the material B, as seen from FIG. 9, the real part ε₁ ofthe complex dielectric function takes the zero value when thewave-number is nearly 14,500 cm⁻¹. As seen from FIG. 10, however, thecurve representing the imaginary part a₂ has no such distinct peak asFIG. 8 shows in the vicinity of 14,500 cm⁻¹. As seen from FIG. 10,moreover, the imaginary part a₂ has a gentle peak in the vicinity of8,000 cm⁻¹. In FIG. 9, however, ε₁ does not take t;he zero value in thevicinity of 8,000 cm⁻¹.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a conceptual diagram of a conventional La₂ CuO₄superconductor;

FIG. 2 is a conceptual diagram of a conventional. Y₁ Ba₂ Cu₃ O₇superconductor;

FIG. 3 is a conceptual diagram of a conventional Bi₂ Sr₂ Ca₂ Cu₃ O₁₀superconductor;

FIG. 4 is a conceptual diagram of a one-layer system oxidesuperconductor according to the present invention;

FIG. 5 is a conceptual diagram of a two-layer system oxidesuperconductor according to the present invention;

FIG. 6 is a conceptual diagram of a three-layer system oxidesuperconductor according to the present invention;

FIG. 7 is a graph showing the relationships between real and imaginaryparts ε1 and ε2 of the complex dielectric function of the oxidesuperconductor and the measurement wave-number;

FIG. 8 is a graph showing the relationships between real and imaginaryparts a1 and a2 of kite reciprocal function of the complex dielectricfunction of the oxide superconductor and measurement wave-number;

FIG. 9 is a graph showing the relationships between the real andimaginary parts ε1 and ε2 of the complex dielectric function of thenon-superconducting oxide material and the measurement wave-number;

FIG. 10 is a graph showing the relationships between real and imaginaryparts a1 and a2 of the reciprocal function of the complex dielectricfunction of the non-superconducting oxide material and the measurementwave-number;

FIG. 11 is a model diagram of a crystal structure (Model 1-4) ofEmbodiment 3 as a one-layer system oxide superconductor according to thepresent invention;

FIG. 12 is an X-ray diffraction pattern diagram of the oxidesuperconductor of Embodiment 3;

FIG. 13 is a model diagram of a crystal structure (Model 1-15) ofEmbodiment 8 as a one-layer system oxide superconductor according to thepresent invention;

FIG. 14 is an X-ray diffraction pattern diagram of the oxidesuperconductor of Embodiment 8;

FIG. 15 is a model diagram of a crystal structure (Model 1-16) ofEmbodiment 9 as a one-layer system oxide superconductor according to thepresent invention;

FIG. 16 is an X-ray diffraction pattern diagram of the oxidesuperconductor of Embodiment 9;

FIG. 17 is a model diagram of a crystal structure (Model 1-17) ofEmbodiment 10 as a one-layer system oxide superconductor according tothe present invention;

FIG. 18 is an X-ray diffraction pattern diagram of the oxidesuperconductor of Embodiment 10;

FIG. 19 is a model diagram of a crystal structure (Model 2-6) ofEmbodiment 15 as a two-layer system oxide superconductor according tothe present invention;

FIG. 20 is an X-ray diffraction pattern diagram of the oxidesuperconductor of Embodiment 15;

FIG. 21 is a model diagram of a crystal structure (Model 2-8) ofEmbodiment 17 as a two-layer system oxide superconductor according tothe present invention;

FIG. 22 is an X-ray diffraction pattern diagram of the oxidesuperconductor of Embodiment 17;

FIG. 23 is a model diagram of a crystal structure (Model 2-11) ofEmbodiment 18 as a two-layer system oxide superconductor according tothe present invention;

FIG. 24 is an X-ray diffraction pattern diagram of the oxidesuperconductor of Embodiment 18;

FIG. 25 is a model diagram of a crystal structure (Model 3-5) ofEmbodiment 27 as a three-layer system oxide superconductor according tothe present invention;

FIG. 26 is an X-ray diffraction pattern diagram of the oxidesuperconductor of Embodiment 27;

FIG. 27 is a model diagram of a crystal structure (Model 3-10) ofEmbodiment 30 as a three-layer system oxide superconductor according tothe present invention;

FIG. 28 is an X-ray diffraction pattern diagram of the oxidesuperconductor of Embodiment 30;

FIG. 29 is a model diagram of a crystal structure (Model 3-20) ofEmbodiment 32 as a three-layer system oxide superconductor according tothe present invention; and

FIG. 30 is an X-ray diffraction pattern diagram of the oxidesuperconductor of Embodiment 32.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1

Powders of PbO and CuO were weighed so that the molar ratio Pb:Cu was2:1, and these powders were mixed together. The resulting powder mixturewas pressed into pellets at 500 kg/cm², and the resulting pellet wasthen sintered for 5 hours in air at 800° C.

Composition: A sintered pellet of Pb₂ CuO_(x) was obtained. This will bereferred to as sintered body I.

Powders of SrCO₃, La₂ (CO₃)₃.nH₂ O, and CuO were weighed so that themolar ratio Sr:La:Cu was 0.75:0.25:1, and these powders were mixedtogether. The resulting powder mixture was pressed into pellets at 500kg/cm², and the resulting pellet was then sintered for 5 hours in air at900° C.

Composition: A sintered pellet of Sr₀.75 La₀.25 CuO_(x) was obtained.This will be referred to as sintered body II.

Powders of CaCO₃, Y₂ O₃, and CuO were weighed so that the molar ratioCa:Y:Cu was 0.8:0.2:1, and these powders were mixed together. Theresulting powder mixture was pressed into pellets at 500 kg/cm², and theresulting pellet was then sintered for 5 hours air at 900° C.

Composition: A sintered pellet of Ca₀.8 Y₀.2 CuO_(x) was obtained. Thiswill be referred to as sintered body III.

Powders of La₂ (CO₃)₃.nH₂ O, BaCO₃, PbO, and CuO were weighed so thatthe molar ratio La:Ba:Pb:Cu was 3:0.75:0.5:2, and these powders weremixed together. The resulting powder mixture was pressed into pellets;at 500 kg/cm², and the resulting pellet was then sintered for 5 hours inair at 900° C.

Composition: A sintered pellet of La₃ Ba₀.75 Pb₀.25 Cu₂ O_(x) wasobtained. This will be referred to as sintered body IV.

Then, these sintered bodies I, II, III and IV were set individually ontarget holder which was located in a vacuum chamber, an MgO (100) singlecrystal substrate was set in a position opposite to these sinteredbodies, and this substrate was heated to 600° C.

O₂ gas and N₂ O gas were introduced into the vacuum chamber, and anexcimer laser was applied to the respective targets of the individualsintered bodies with the degree of vacuum in the chamber kept at 5×10⁻⁴Torr (oxygen partial pressure: 2.5×10⁻⁴ Torr).

The intensity of the laser used was 150 mJ/pulse. The laser was appliedto the respective targets of sintered bodies in a manner such that thesintered bodies I, II, III, IV, III and II were irradiated for eachcycle in the order named, and this cycle was repeatedly executed.

A film was formed on the MgO substrate. After the film formation, thesubstrate was cooled at the rate of 20° C./min by introducing oxygen gascontaining 8% by volume of ozone into the chamber at the flow rate of 25ml/min.

The general composition of the film obtained was (Pb₀.5 Cu₀.5) (Sr₀.75La₀.25)₂ (La₀.75 Ba₀.19 Pb₀.06)₂ (Ca₀.8 Y₀.2)₂ Cu₅ O₁₃.2. When an X-raydiffraction spectrum was observed, the crystal structure of the filmproved to be identical with that of the aforementioned Model No. 2-16.

Subsequently, real and imaginary parts ε1 and ε2 of the complexdielectric function of this film were measured at room temperature bythe aforesaid spectroellipsometry. Thereupon, the value ε1 proved to bezero when the measurement wave-number was about 9,500 cm⁻¹, and also, apeak was observed in a curve of an imaginary part a2 of a reciprocalfunction when the wave-number was about 9,500 cm⁻¹.

Thus, it was confirmed that this film is a two-layer system oxidesuperconductor as it is called according to the present invention.

Embodiments 2 to 35

Sintered bodies of various compositions shown in Tables 2-(1) and 2-(2)were manufactured by the powder mixing method in the same manner as inthe case of Embodiment 1.

                                      TABLE 2                                     __________________________________________________________________________            Type of Sintered Body (Target)                                                I             II        III       IV                                  __________________________________________________________________________    Embodiment 2                                                                          La Ba.sub.0.75 Pb.sub.0.5 O.sub.x                                                           Cu O.sub.2                                                                              Ba.sub.1.9 La.sub.0.1 Cu                                                                --sub.x                             Embodiment 3                                                                          Bi.sub.1.6 Pb.sub.0.8 O.sub.x                                                               Sr Cu O.sub.x                                                                           La.sub.1.6 Ba.sub.0.2 Pb.sub.0.6 Cu                                           O.sub.x   --                                  Embodiment 4                                                                          Bi.sub.1.6 Pb.sub.0.6 O.sub.x                                                               Sr.sub.0.7 La.sub.0.3 Cu O.sub.x                                                        Ba.sub.1.8 La.sub.0.2 Cu                                                                --sub.x                             Embodiment 5                                                                          Bi.sub.1.6 Pb.sub.0.6 O.sub.x                                                               Sr.sub.0.7 La.sub.0.3 Cu O.sub.x                                                        Ba.sub.1.7 La.sub.0.3 Cu.sub.2 O.sub.x                                                  --                                  Embodiment 6                                                                          Tl.sub.0.8 Pb.sub.0.4 O.sub.x                                                               Ba Cu.sub.1.1 O.sub.x                                                                   La.sub.1.8 Ba.sub.0.2 Cu                                                                --sub.x                             Embodiment 7                                                                          Tl.sub.0.8 Pb.sub.0.4 O.sub.x                                                               Ba Sr Cu.sub.1.1 O.sub.x                                                                Bi.sub.1.6 Pb.sub.0.6 O.sub.x                                                           --                                  Embodiment 8                                                                          Pb.sub.3 Cu O.sub.x                                                                         Sr Ba Cu O.sub.x                                                                        Tl.sub.0.8 Pb.sub.0.4 O.sub.x                                                           --                                  Embodiment 9                                                                          Pb.sub.0.8 Sr.sub.0.5 La.sub.0.5 Cu.sub.1.5 O.sub.x                                         Cu O.sub.x                                                                              La.sub.1.8 Ba.sub.0.2 Cu                                                                --sub.x                             Embodiment 10                                                                         Pb.sub.1.0 Sr.sub.0.5 La.sub.0.5 Cu.sub.2 O.sub.x                                           Ba.sub.2 Cu O.sub.x                                                                     --        --                                  Embodiment 11                                                                         Bi.sub.2 O.sub.x                                                                            Sr La Cu O.sub.x                                                                        Pb.sub.0.5 Cu.sub.0.5 O.sub.x                                                           --                                  Embodiment 12                                                                         La.sub.1.4 Ba.sub.0.4 Pb.sub.0.6 Cu O.sub.x                                                 Ca.sub.0.7 Y.sub.0.3 Cu O.sub.x                                                         Ba.sub.1.8 La.sub.1.2 Cu                                                                --sub.x                             Embodiment 13                                                                         La.sub.1.8 Ba.sub.0.2 Pb.sub.0.3 Cu O.sub.x                                                 Ca.sub.0.1 Y.sub.0.9 Cu O.sub.x                                                         Ba.sub.0.9 La.sub.0.1 Cu                                                                --sub.x                             Embodiment 14                                                                         Bi.sub.2 Sr.sub.0.9 La.sub.0.1 Cu O.sub.x                                                   Ca.sub.0.5 Y.sub.0.5 Cu O.sub.x                                                         Ba.sub.1.8 La.sub.0.2 Cu                                                                --sub.x                             Embodiment 15                                                                         Bi.sub.2 Sr.sub.0.7 La.sub.0.3 Cu O.sub.x                                                   Ca.sub.0.8 Y.sub.0.2 Cu O.sub.x                                                         Ba Cu O.sub.x                                                                           --                                  Embodiment 16                                                                         Tl.sub.2 Ba.sub.0.9 La.sub.0.1 Cu O.sub.x                                                   Ca.sub.0.9 Ho.sub.0.1 Cu O.sub.x                                                        Ba.sub.0.9 La.sub.0.1 Cu                                                                --sub.x                             Embodiment 17                                                                         tl.sub.1.5 Sr.sub.0.9 Ba.sub.0.05 La.sub. 0.05 Cu                                           Ca.sub.0.95 Y.sub.0.05 Cu O.sub.x                                                       Ba.sub.0.9 Sr.sub.0.1 Cu                                                                --sub.x                             Embodiment 18                                                                         Pb.sub.3 Cu O.sub.x                                                                         Sr.sub.0.7 La.sub.0.3 Cu O.sub.x                                                        Ca.sub.0.9 Nd.sub.0.1 Cu                                                                La.sub.1.8 Ba.sub.0.2 Cu                                                      O.sub.x                             Embodiment 19                                                                         Pb.sub.0.5 Cu.sub.0.5 O.sub.x                                                               Sr.sub.0.5 La.sub.0.5 Cu O.sub.x                                                        Ca.sub.0.8 Y.sub.0.2 Cu                                                                 Bi.sub.2 Sr La Cu O.sub.x           Embodiment 20                                                                         La.sub.1.8 Ba.sub.0.2 Cu O.sub.x                                                            Ca.sub.0.9 Sr.sub.0.1 Cu O.sub.x                                                        Nd.sub.1.6 Ce.sub.0.4 Cu                                                                --sub.x                             Embodiment 21                                                                         Ba.sub.1.8 La.sub.2 Cu.sub.2 O.sub.x                                                        Ca.sub.0.8 Gd.sub.0.2 Cu O.sub.x                                                        Nd.sub.1.6 Ce.sub.0.4 Cu                                                                --sub.x                             Embodiment 22                                                                         Bi Sr Cu O.sub.x                                                                            Ca Cu O.sub.x                                                                           Nd.sub.1.6 Ce.sub.0.4 Cu                                                                --sub.x                             Embodiment 23                                                                         Tl.sub.2 Ba.sub.0.8 La.sub.0.2 Cu O.sub.x                                                   Ca.sub.0.95 Sr.sub.0.05 Cu O.sub.x                                                      Eu.sub.1.6 Ce.sub.0.4 Cu                                                                --sub.x                             Embodiment 24                                                                         Pb Cu Sr.sub.1.6 La.sub.0.4 Cu.sub.2 O.sub.x                                                Ca.sub.0.8 Er.sub.0.2 Cu O.sub. x                                                       Gd.sub.1.6 Ce.sub.0.4 Cu                                                                --sub.x                             Embodiment 25                                                                         La.sub.0.8 Ba.sub.0.1 Pb.sub.0.3 Cu O.sub.x                                                 Ca.sub.0.7 Y.sub.0.3 Cu O.sub.x                                                         Ba.sub.1.8 Sr.sub.0.2 Cu.sub.2 O.sub.x                                                  --                                  Embodiment 26                                                                         La.sub.0.8 Ba.sub.0.1 Pb.sub.0.3 Cu O.sub.x                                                 Ca.sub.0.7 Y.sub.0.3 Cu O.sub.x                                                         Ba.sub.0.9 Sr.sub.0.1 Cu.sub.3 O.sub.x                                                  --                                  Embodiment 27                                                                         Bi.sub.2 O.sub.x                                                                            Sr.sub.0.7 La.sub.0.3 Cu O.sub.x                                                        Ca.sub.0.9 Y.sub.0.1 Cu                                                                 Ba.sub.1.9 La.sub.0.1 Cu.sub.3                                                O.sub.x                             Embodiment 28                                                                         Bi.sub.2 O.sub.x                                                                            Sr.sub.0.9 La.sub.0.1 Cu O.sub.x                                                        Ca.sub.0.9 Y.sub.0.1 Cu                                                                 Ba.sub.1.9 La.sub.0.1 Cu.sub.3                                                O.sub.x                             Embodiment 29                                                                         TlO.sub.x     Ba.sub.0.9 Sr.sub.0.1 Cu O.sub.x                                                        Ca.sub.0.95 Ho.sub.0.05 Cu                                                              Ba.sub.1.9 La.sub.0.1 Cu.sub.3                                                O.sub.x                             Embodiment 30                                                                         Bi.sub.1.6 Pb.sub.0.8 Sr.sub.1.7 La.sub.0.2 Cu.sub.2 O.sub.x                                Ca.sub.0.9 Y.sub.0.1 Cu O.sub.x                                                         Tl.sub.3.2 Ba.sub.2 Cu.sub.2 O.sub.x                                                    --                                  Embodiment 31                                                                         Pb.sub.2.5 Sr.sub.1.4 La.sub.0.7 Cu.sub.2 O.sub.x                                           Ca.sub.0.5 Sm.sub.0.5 Cu O.sub.x                                                        Bi.sub.2 Sr.sub.1.4 La.sub.0.6 Cu.sub.2                                       O.sub.x   --                                  Embodiment 32                                                                         Pb.sub.0.8 Cu.sub.1.5 Sr.sub.0.5 La.sub.0.5 O.sub.x                                         Ca.sub.0.7 Y.sub.0.3 Cu O.sub.x                                                         TlBa.sub.2 Cu O.sub.x                                                                   --                                  Embodiment 33                                                                         Ba.sub.1.9 La.sub.0.1 Cu.sub.3 O.sub.x                                                      Ca.sub.0.1 Gd.sub.0.9 Cu O.sub.x                                                        Nd.sub.1.6 Ce.sub.0.4 Cu                                                                --sub.x                             Embodiment 34                                                                         Bi.sub.1.6 Pb.sub.0.6 O.sub.x                                                               Sr.sub.0.95 Ba.sub.0.05 Cu O.sub.x                                                      Ca.sub.0.9 Y.sub.0.1 Cu                                                                 Sm.sub.1.6 Ce.sub.0.4 Cu                                                      O.sub.x                             Embodiment 35                                                                         Pb Cu.sub.0.5 O.sub.x                                                                       Sr.sub.0.5 La.sub.0.5 Cu O.sub.x                                                        Ca Cu O.sub.x                                                                           Eu.sub.1.6 Ce.sub.0.4 Cu            __________________________________________________________________________                                              O.sub.x                         

Then, films were formed on substrates shown in Tables 3-(1) and 3-(2) bythe laser deposition method using these sintered bodies as targets, andthese films were heat-treated under the oxygen partial pressure in thesame manner as in Embodiment 1.

During the film formation, an excimer laser was applied to the targetsby repeating the cycles shown in Tables 3-(1) and 3-(2).

Tables 3-(1) and 3-(2) show the respective general compositions of thefilms obtained, and also show models of crystal structures obtainedX-ray diffraction patterns.

A spectroellipsometry measurement was made on each of these films in thesame manner as in Embodiment 1. Thereupon, the curve of the real part ε₁of the complex dielectric function ε₁ passed the zero value, and a peakwas observed in the curve of the imaginary part a2 of its reciprocalfunction at the wave-number which gave ε₁ =0 in the aforesaid complexdielectric function. Thus, it was confirmed that the films aresuperconducting materials.

                                      TABLE 3                                     __________________________________________________________________________                                                     Crystal                              Type of                     Cycle of Laser                                                                             Structure                            Substrate                                                                           General Composition of Film                                                                         Application to Target                                                                      Model                        __________________________________________________________________________    Embodiment 2                                                                          Sr Ti O.sub.3                                                                       (LA, Ba, Pb).sub.2 (Ba, La).sub.2 Cu.sub.3 O.sub.8.3                                                I→II→III→II.fwdar                                        w.           1-1                          Embodiment 3                                                                          Sr Ti O.sub.3                                                                       (Bi, Pb).sub.2 Sr.sub.2 La.sub.2 Cu.sub.2 O.sub.10                                                  II→III→II→I.fwdar                                        w.           1-4                          Embodiment 4                                                                          Sr Ti O.sub.3                                                                       (Bi, Pb).sub.2 (Sr, La).sub.2 (Ba, La).sub.2 Cu.sub.3                         O.sub.10.8            II→I→II→III.fwdar                                        w.           1-5                          Embodiment 5                                                                          La Al O.sub.3                                                                       (Bi, Pb).sub.2 (Sr, La).sub.2 (Ba, La).sub.2 Cu.sub.4                         O.sub.11.7            II→I→II→III.fwdar                                        w.           1-6                          Embodiment 6                                                                          Mg O  (Tl, Pb).sub.2 Ba.sub.2 La.sub.2 Cu.sub.2 O.sub.10                                                  III→II→I→II.fwdar                                        w.           1-7                          Embodiment 7                                                                          Sr Ti O.sub.3                                                                       (Tl, Pb).sub.2 (Bi, Pb).sub.2 (Sr, Ba).sub.2 Sr.sub.2                         Cu.sub.2 O.sub.12     II→III→II→I.fwdar                                        w.           1-10                         Embodiment 8                                                                          Mg O  Pb.sub.2  (Sr, Ba).sub.2 Ba.sub.2 (Tl, Pb).sub.2 Cu.sub.3                     O.sub.12              II→I→II→III.fwdar                                        w.           1-15                         Embodiment 9                                                                          Sr Ti O.sub.3                                                                       (Pb, Cu) (Sr, La).sub.2 (La, Ba).sub.2 Cu.sub.2 O.sub.8.9                                           I→II→III→II.fwdar                                        w.           1-16                         Embodiment 10                                                                         Sr Ti O.sub.3                                                                       (Pb, Cu) (Sr, La).sub.2 Ba.sub.2 Cu.sub.3 O.sub.10.1                                                I→II→                                                                        1-17                         Embodiment 11                                                                         Sr Ti O.sub.3                                                                       (Pb, Cu) (Sr, La).sub.4 Bi.sub.2 Cu.sub.2 O.sub.10.9                                                II→I→II→III.fwdar                                        w.           1-19                         Embodiment 12                                                                         La Ga O.sub.3                                                                       (La, Ba, Pb).sub.2 (Ba, La).sub.2 (Ca, Y).sub.2 Cu.sub.5                      O.sub.12.5            I→II→III→II.fwdar                                        w.           2-1                          Embodiment 13                                                                         Sr Ti O.sub.3                                                                       (Ba, La).sub.2 (La, Ba, Pb).sub.2 Ca, Y).sub.2 Cu.sub.6                       O.sub.13.5            I→II→III→II.fwdar                                        w.           2-2                          Embodiment 14                                                                         Nd Al O.sub.3                                                                       Bi.sub.2 (Sr, La).sub.2 (Ba, La).sub.2 (Ca, Y).sub.2                          Cu.sub.5 O.sub.15     I→II→III→II.fwdar                                        w.           2-5                          Embodiment 15                                                                         Mg O  Bi.sub.2 (Sr, La).sub.2 Ba.sub.2 (Ca, Y).sub.2 Cu.sub.6                       O.sub.15.7            I→II→III→II.fwdar                                        w.           2-6                          Embodiment 16                                                                         Sr Ti O.sub.3                                                                       Tl.sub.2 (Ba, La).sub.4 (Ca, Ho).sub.2 Cu.sub.5 O.sub.13.5                                          I→II→III→II.fwdar                                        w.           2-8                          Embodiment 17                                                                         LA Al O.sub.3                                                                       (Tl, Pb) (Sr, La, Ba).sub.4 (Ca, Y).sub.2 Cu.sub.5 O.sub.12.                  5                     III→II→I→II.fwdar                                        w.           2-8                          Embodiment 18                                                                         Mg O  Pb.sub.2 (Sr, La).sub.2 La.sub.2 (Ca, Nd).sub.2 Cu.sub.5                      O.sub.14              II→I→II→III.fwdar                                        w.IV→III→                                                                    2-11                         Embodiment 19                                                                         Mg O  (Pb, Cu) (Sr, La).sub.4 Bi.sub.2 (Ca, Y).sub.2 Cu.sub.4                       O.sub.14.8            IV→III→II→I.fwdar                                        w.II→III→                                                                    2-19                         Embodiment 20                                                                         Sr Ti O.sub.3                                                                       (Nd, Ce).sub.2 (La, Ba).sub.2 (Ca, Sr).sub.2 Cu.sub.4                         O.sub.12              I→II→III→II.fwdar                                        w.           2-22                         Embodiment 21                                                                         Sr Ti O.sub.3                                                                       (Sm, Ce).sub.2 (Ba, La).sub.2 (Ca, Gd).sub.2 Cu.sub.5                         O.sub.13              I→II→III→II.fwdar                                        w.           2-23                         Embodiment 22                                                                         Sr Ti O.sub.3                                                                       (Nd, Ce).sub.2 Sr.sub.2 Bi.sub.2 Ca.sub.2 Cu.sub.4 O.sub.13.                  6                     III→II→I→II.fwdar                                        w.           2- 25                        Embodiment 23                                                                         Mg O  (Eu, Ce).sub.2 (Ba, La).sub.2 Tl.sub.2 (Ca, Sr).sub.2                         Cu.sub.4 O.sub.14     I→II→III→II.fwdar                                        w.           2-26                         Embodiment 24                                                                         Sr Ti O.sub.3                                                                       (Gd, Ce).sub.2 (Sr, La).sub.2 (Pb, Cu) (Ca, Er).sub.2                         Cu.sub.4 O.sub.18     I→II→III→II.fwdar                                        w.           2-28                         Embodiment 25                                                                         La Ga O.sub.3                                                                       (La, Ba, Pb).sub.2 Ba.sub.2 (Ca, Y).sub.4 Cu.sub.7 O.sub.16.                  5                     I→II→III→II.fwdar                                        w.           3-1                          Embodiment 26                                                                         Sr Ti O.sub.3                                                                       (La, Ba, Pb).sub.2 Ba.sub.2 (Ca, Y).sub.4 Cu.sub.7 O.sub.18.                  8                     I→II→III→II.fwdar                                        w.           3-2                          Embodiment 27                                                                         Sr Ti O.sub.3                                                                       Bi.sub.2 (Sr, La).sub.2 (La, Ba).sub.2 (Ca, Y).sub.4                          Cu.sub.7 O.sub.18.8   II→I→II→III.fwdar                                        w.IV→III→                                                                    3-5                          Embodiment 28                                                                         Sr Ti O.sub.3                                                                       Bi.sub.2 (Sr, La).sub.2 (La, Ba).sub.2 (Ca, Y).sub.4                          Cu.sub.8 O.sub.20     II→I→II→III.fwdar                                        w.IV→III→                                                                    3-6                          Embodiment 29                                                                         Nd Ga O.sub.3                                                                       Tl (Ba, Sr, La).sub.4 (kCa, Ho).sub.4 Cu.sub.8                                                      II→I→II→III.fwdar                                        w. IV→III→                                                                   3-9                          Embodiment 30                                                                         Sr Ti O.sub.3                                                                       (Bi, Pb).sub.2 Tl.sub.2 (Ba, Sr, La).sub.4 (Ca, Y).sub.4                      Cu.sub.6 O.sub.20.2   I→II→III→II.fwdar                                        w.           3-10                         Embodiment 31                                                                         Mg O  Pb.sub.2 (Sr, La).sub.4 Bi.sub.2 (Ca, Sm).sub.4 Cu.sub.7                      O.sub.20              III→II→I→II.fwdar                                        w.           3-14                         Embodiment 32                                                                         Mg O  (Pb, Cu) (Sr, La).sub.2 Ba.sub.2 Tl (Ca, Y).sub.4 Cu.sub.6                    O.sub.18              I→II→III→II.fwdar                                        w.           3-20                         Embodiment 33                                                                         Sr Ti O.sub.3                                                                       (Nd, Ce).sub.2 (Ba, La).sub.2 (Ca, Gd).sub.4 Cu.sub.8                         O.sub.18              III→II→I→II.fwdar                                        w.           3-24                         Embodiment 34                                                                         Sr Ti O.sub.3                                                                       (Sm, Ce).sub.2 Sr.sub.2 (Bi, Pb).sub.2 (Ca, Y).sub.4                          Cu.sub.6 O.sub.18     II→I→II→III.fwdar                                        w.IV→III→                                                                    3-25                         Embodiment 35                                                                         Sr Ti O.sub.3                                                                       (Eu, Ce).sub.2 (Sr, La).sub.2 (Pb, Cu)Ca.sub.4 Cu.sub.6                       O.sub.16.7            IV→III→II→I.fwdar                                        w.II→III→                                                                    3-28                         __________________________________________________________________________

Among these 34 kinds of superconducting films, Embodiments 2 to 11 wereone-layer system oxide superconductors, Embodiments 12 to 24 weretwo-layer system oxide superconductors, and Embodiments 25 to 35 werethree-layer system oxide superconductors.

The following is a description of model figures of the respectivetypical crystal structures of the one-, two-, and three-layer systems,among these individual superconductors, and X-ray diffraction patterncorresponding individually to the structures.

First, FIGS. 11 to 18 show details of the one-layer systems, in whichFIGS. 11 and 12 are a model diagram and an X-ray diffraction pattern,respectively, of Embodiment 3 (Model 1-4), FIGS. 13 and 14 are a modeldiagram and an X-ray diffraction pattern, respectively, of Embodiment 8(Model 1-1.5). FIGS. 15 and 16 are a model diagram and an X-raydiffraction pattern, respectively, of Embodiment 9 (Model 1-16), andFIGS. 17 and 18 are a model diagram and an X-ray diffraction pattern,respectively, of Embodiment 10 (Model 1-17).

FIGS. 19 to 24 show details of the two-layer systems, in which FIGS. 19and 20 are a model diagram and an X-ray diffraction pattern,respectively, of Embodiment 15 (Model 2-6), FIGS. 21 and 22 are a modeldiagram and an X-ray diffraction pattern, respectively, of Embodiment 17(Model 2-8), and FIGS. 23 and 24 are a model diagram and an X-raydiffraction pattern, respectively, of Embodiment 18 (Model 2-11).

Further, FIGS. 25 to 30 show details of the three-layer systems, inwhich FIGS. 25 and 26 are a model diagram and an X-ray diffractionpattern, respectively, of Embodiment 27 (Model 3-5), FIGS. 27 and 28 area model diagram and an X-ray diffraction pattern, respectively, ofEmbodiment 30 (Model 3-10), and FIGS. 29 and 30 are a model diagram andan X-ray diffraction pattern, respectively, of Embodiment 32 (Model3-20).

Practically, also in the individual crystal structures shown in thesemodel figures, the oxygen content may be somewhat deviated from itsstoichiometric value, due to carrier concentration adjustment, or somecations may be substituted, as mentioned above.

Although only thirty-five kinds of oxide superconductors of the presentinvention, among seventy-seven kinds in total, have been given as theembodiments, the remaining kinds can be also manufactured by the samemethod as these embodiments.

Thus, according to the present invention, the approximately twenty kindsof conventionally found copper oxide superconductors can be increased toabout seventy-seven kinds by using a combination of two blocking layersof different compositions and one CuO₂ sheet, a combination of twoblocking layers of different compositions, one mediating layer, and twoCu-O₂ sheets, or a combination of two blocking layers of differentcompositions, two mediating layers, and three Cu-O₂ sheets, as has beenalso described in connection with the embodiments, so that the materialscan be applied to a wider variety of fields.

We claim:
 1. An oxide superconductor comprising repeated units eachincluding a first blocking layer having a composition selected from thefollowing group, a first Cu-O₂ sheet, a second blocking layer having acomposition selected from the following group and different from thecomposition of said first blocking layer, and a second Cu-O₂ sheet,arranged in layers in the order named,said group consisting of:La₂ O₂,BaO-CuO-BaO BaO-CuO-CuO-BaO SrO-Bi₂ O₂ -SrO, BaO-Tl₂ O₂ -BaO,BaO-TlO-BaO, SrO-PbO-Cu-PbO-SrO, SrO-(Pb, Cu)O-SrO, and SrO-(Pb, St)O-SrO.
 2. An oxide superconductor comprising repeated units eachincluding a first blocking layer having a composition selected from thefollowing group a, a first Cu-O₂ sheet, a first mediating layerconsisting of elements selected from the following group b, a secondCu-O₂ sheet, a second blocking layer having a composition selected fromthe following group a and different from the composition of said firstblocking layer, a third Cu-O₂ sheet, a second mediating layer consistingof elements selected from the following group b, and a fourth Cu-O₂sheet, arranged in layers in the order named,said group a consistingof:La₂ O₂, BaO-CuO- BaO, SrO-Bi₂ O₂ -SrO, BaO-Tl₂ O₂ -BaO, BaO-Tl₂ O₂-BaO, SrO-PbO-Cu-PbO-SrO, SrO-(Pb, Cu)O-SrO, SrO-(Pb, Sr)O-SrO, and Ln₂O₂ (where Ln is selected from Nd, Sm, Eu and Gd), said group bconsisting of:Ca, Y, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm and Yb
 3. An oxidesuperconducting material comprising repeated units each including afirst blocking layer having a composition selected from the followinggroup a, a first Cu-O₂ sheet, a first mediating layer consistingelements selected from the following group b, a second Cu-O₂ sheet, asecond mediating layer consisting of elements selected from thefollowing group b, a third Cu-O₂ sheet, a second blocking layer having acomposition selected from the following group a and different from thecomposition of said first blocking layer, a fourth Cu-O₂ sheet, a thirdmediating layer consisting of elements selected from the following groupb, a fifth CuO₂ sheet, a fourth mediating layer consisting of elementsselected from the following group b, and a sixth Cu-O₂ sheet, arrangedin layers in the order named,said group a consisting of:La₂ O₂,BaO-CuO-BaO, BaO-CuO-CuO-BaO, SrO-Bi₂ O₂ -SrO, BaO-Tl₂ O₂ -BaO,BaO-TlO-BaO, SrO-PbO-Cu-PbO-SrO, SrO-(Pb, Cu)O-SrO, SrO-(Pb, Sr)O-Sr,and Ln₂ O₂ (where Ln is selected from Nd, Sm, Eu and Gd), said group bconsisting of: Ca, Sr, Y, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb and Lu. 4.An oxide superconductor comprising repeated units each including a firstblocking layer having a composition selected from the following group a,a first Cu-O₂ sheet, a first mediating layer consisting of elementsselected from the following group b, a second Cu-O₂ sheet, a secondblocking layer having a composition selected from the following group aand different from the composition of said first blocking layer, a thirdCu-O₂ sheet, a second mediating layer consisting of elements selectedfrom the following group b and a fourth Cu-O₂ sheet, arranged in layersin the order named,said group a consisting of:La₂ O₂, BaO-CuO-BaO,BaO-CuO-CuO-BaO, SrO-Bi₂ O₂ -SrO, BaO-Tl₂ O₂ -BaO, BaO-TlO-BaO,SrO-PbO-Cu-PbO-SrO, SrO-(Pb, Cu)O-SrO, SrO-(Pb, Sr)O-SrO, and Ln₂ O₂(where Ln is selected from Nd, Sm, Eu and Gd), said group b consistingof:Sr and Lu.
 5. An oxide superconductor comprising repeated units eachincluding a first blocking layer having a composition selected from thefollowing group a, a first Cu-O₂ sheet, a first mediating layerconsisting of elements selected from the following group b, a secondCu-O₂ sheet, a second blocking layer having a composition selected fromthe following group a and different from the composition of said firstblocking layer, a third Cu-O₂ sheet, a second mediating layer consistingof elements selected from the following group b, and a fourth Cu-O₂sheet, arranged in layers in the order named,said group a consistingof:La₂ O₂, BaO-CuO-CuO-BaO, SrO-Bi₂ O₂ -SrO, BaO-Tl₂ O₂ -BaO,BaO-TlO-BaO, SrO-PbO-Cu-PbO-SrO, SrO-(Pb, Cu)O-SrO, SrO-(Pb, Sr)O-SrO,and Ln₂ O₂ (where Ln is selected from Nd, Sm, Eu and Gd), said group bconsisting of:Ca, Y, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm and Yb.